Information storage medium storing graphic data and apparatus and method of processing the graphic data

ABSTRACT

An information storage medium including graphic data and presentation information, and an apparatus and method of processing the graphic data are provided. The information storage medium includes the graphic data, page composition information which defines page composition of the graphic data, and the presentation information indicating when graphic screen data, which is composed with reference to the page composition information of the graphic data, is output to a display screen. Therefore, a graphic object is reusable in graphic data processing, and accordingly, a time taken to process the graphic data is reducible and memory area may be saved.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 10/890,212filed on Jul. 14, 2004, and claims the benefit of Korean PatentApplication No. 2003-53073 filed on Jul. 31, 2003, in the KoreanIntellectual Property Office, and U.S. Provisional Application No.60/511,110 filed on Oct. 15, 2003, in the U.S. Patent & TrademarkOffice. The disclosures of application Ser. No. 10/890,212, KoreanPatent Application No. 2003-53073, and U.S. Provisional Application No.60/511,110 are incorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to graphic data processing, and moreparticularly, to an information storage medium including graphic datahaving presentation information, and an apparatus and method ofprocessing the graphic data.

2. Description of the Related Art

Various data compression formats are used to transmit video and audiodata through broadcasting or store the video and audio data in a storagemedium. Among the data compression formats, Moving Picture Experts Group(MPEG)-2 transport stream (TS) multiplexes and stores video and audiodata by dividing the video and audio data into packets having apredetermined size. Since graphic data, as well as video data, isdisplayed on a screen, the MPEG-2 TS stored in an information storagemedium includes the graphic data. The graphic data roughly comprisessubtitle graphic data and navigation graphic data.

The graphic data included in the MPEG-2 TS is decoded in a graphic dataprocessing apparatus and output to a display screen. In addition to thegraphic data, the MPEG-2 TS stored in the information storage mediumalso includes time information indicating when the graphic data is to betransmitted to a variety of buffers disposed inside the graphic dataprocessing apparatus, and time information indicating when the graphicdata of a completely composed screen is to be output to the displayscreen. Times indicated by the time information should be properly setso that graphic data processing may be performed efficiently. Further, aconfiguration of the buffers in the graphic data processing apparatusdetermines an efficiency of the graphic data processing apparatus. Aconventional graphic data processing apparatus has a disadvantage inthat the graphic data processing apparatus cannot reuse a graphic objectof which a graphic screen is composed, thereby deteriorating theefficiency in the graphic data processing.

SUMMARY OF THE INVENTION

The present invention provides an information storage medium includinggraphic data that newly defines presentation information includedtherein to improve an efficiency in graphic data processing, and anapparatus and method of processing the graphic data.

Additional aspects and/or advantages of the invention will be set forthin part in the description which follows and, in part, will be obviousfrom the description, or may be learned by practice of the invention.

According to an aspect, an information storage medium is providedcomprising: graphic data; page composition information which describes apage composition of the graphic data; and presentation informationindicating when graphic screen data, which is composed with reference tothe page composition information of the graphic data, is output to adisplay screen.

According to another aspect, an information storage medium is providedcomprising: a graphic object of which a graphic data screen is composed;and presentation information indicating when the graphic object isdecoded and output or when the graphic object is input to a decoder.

According to another aspect, an information storage medium is providedcomprising graphic data having a structure thereof which includes adisplay set comprising: a page composition segment which includesinformation on a composition of a graphic screen and a firstpresentation time stamp value; an object display segment which includesa graphic object of which the graphic screen is composed, informationabout a size of the graphic object, and a second presentation time stampvalue; and an end segment which indicates an end of the display set,wherein a first presentation time stamp value indicates when graphicscreen data composing the page composition segment and the objectdisplay segment are output to a display device.

According to another aspect, an information storage medium is providedcomprising graphic data having a structure thereof which includes adisplay set comprising: a page composition segment which includesinformation on a composition of a graphic screen and a firstpresentation time stamp value; an object display segment which includesa graphic object of which the graphic screen is composed, informationabout a size of the graphic object, and a second presentation time stampvalue; and an end segment which indicates an end of the display set,wherein a second presentation time stamp value indicates when thegraphic object is decoded and output.

According to another aspect, an apparatus for processing graphic data isprovided, the apparatus comprising: a first buffer which distinguishesdecoded graphic object data by identifiers of graphic objects and storesthe distinguished graphic object data; and a second buffer whichreceives a graphic object used in a screen composition among the graphicobject data stored in the first buffer and stores graphic screeninformation composed with reference to page composition information.

According to still another aspect, an apparatus for processing graphicdata is provided, the apparatus comprising: a coded data buffer whichreceives and stores coded graphic data and outputs the coded graphicdata according to presentation information included in the graphic data;a decoder which decodes the coded graphic data; a page compositionbuffer which stores page composition information among the decodedgraphic data; a first buffer which stores objects of the decoded graphicdata by graphic object identifiers; a second buffer which receives agraphic object used in a screen composition among the graphic objectsstored in the first buffer and stores graphic screen informationcomposed with reference to the page composition information; and animage controller which receives the page composition information storedin the page composition buffer and controls the graphic objects to betransmitted from the first buffer to the second buffer.

According to another aspect, a method of processing graphic data isprovided, the method comprising: receiving the graphic data; receivingpage composition information which describes a page composition of thegraphic data; and outputting graphic screen data, which is composed withreference to the page composition information of the graphic data, to adisplay screen according to presentation information indicating a timewhen graphic screen data is output to the display screen.

According to another aspect, a method of processing graphic data isprovided, the method comprising: receiving a graphic object of which agraphic data screen is composed; and outputting a decoded graphic objectaccording to presentation information indicating when the graphic objectis decoded and output or when the graphic data is input to a decoder.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects and advantages of the invention will becomeapparent and more readily appreciated from the following description ofthe embodiments, taken in conjunction with the accompanying drawings ofwhich:

FIG. 1 is a diagram illustrating a structure of MPEG-2 TS for graphicdata according to a first embodiment of the present invention;

FIG. 2 is a block diagram of an apparatus for processing graphic dataaccording to a second embodiment of the present invention;

FIG. 3 is a diagram illustrating a third embodiment of the presentinvention of the graphic data;

FIG. 4A is a diagram illustrating a state in which a first display sethaving a page composition segment (PCS) with a page_id=1 is stored inbuffers;

FIG. 4B is a diagram illustrating a state in which a second display sethaving the PCS with the page_id=2 is stored in the buffers;

FIG. 4C is a diagram illustrating a state in which a third display sethaving the PCS with the page_id=3 is stored in the buffers;

FIG. 4D is a diagram illustrating a state in which a fourth display sethaving the PCS with the page_id=4 is stored in the buffers;

FIGS. 5A-5D are diagrams illustrating a process of inputting andoutputting data to and from the buffers in accordance with a passage oftime;

FIG. 6 is a detailed block diagram of a second buffer;

FIG. 7 is a flow chart illustrating a process of outputting graphicdisplay data of a completely composed screen to a display device;

FIG. 8A is a flow chart illustrating a process of outputting a decodedgraphic object; and

FIG. 8B is a flow chart illustrating a process of inputting the graphicobject to a decoder.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Reference will now be made in detail to the embodiments of the presentinvention, examples of which are illustrated in the accompanyingdrawings, wherein like reference numerals refer to the like elementsthroughout. The embodiments are described below to explain the presentinvention by referring to the figures.

Graphic data, which is displayed together with video data, is classifiedinto subtitle graphic data and navigation graphic data. The subtitlegraphic data is screen description data, such as superimposed dialogs,and the navigation graphic data is graphic data regarding menus, such asbuttons used in navigating the video data.

A subtitle graphic data stream and a navigation graphic data stream areprocessed by different graphic data processing apparatuses in a videoreproduction system. However, the graphic data processing apparatuseshave a common configuration. The graphic data processing apparatusesprocess the subtitle graphic data stream and the navigation graphic datastream which are coded in a form of a motion picture experts group(MPEG)-2 transport stream (TS).

FIG. 1 is a diagram illustrating a structure of MPEG-2 TS for graphicdata according to a first embodiment of the present invention.

Referring to FIG. 1, the graphic MPEG-2 TS includes a TS Packet header110 and a data packet 120. The data packet 120 represents subtitlegraphic data and navigation graphic data, and includes display sets 120a through 120 n, which are graphic data groups displayed on one graphicscreen.

The display set 120 a, 120 b . . . or 120 n is a group of graphic dataoutput to one display screen. Referring to FIG. 1, the display set 120a, 120 b . . . or 120 n includes at least two segments. That is, onedisplay set must include a page composition segment (PCS) 121 and an endsegment END 123. An object display segment (ODS) is optionally includedin the display set 120 a, 120 b . . . or 120 n, and a plurality of ODSs122 a through 122 n may be included in the display set 120 a, 120 b . .. or 120 n, if necessary. Each of the different segments will beexplained in detail hereinbelow.

The PCS 121 includes composition information of the ODSs 122 a through122 n displayed on one screen. That is, the PCS 121 includes positioninformation indicating where objects are displayed on the screen andtime information indicating when the objects are output to a displaydevice. The time information is called presentation time stamp (PTS)information. Accordingly, the PCS 121 includes the PTS information. Inan apparatus for processing graphic data which will be described withreference to FIG. 2, the PTS information indicates when graphic screendata, which is composed of the ODSs 122 a through 122 n necessary tocompose one graphic screen, is output from a second buffer 234 to thedisplay device.

The ODSs 122 a through 122 n include subtitle graphic object data andnavigation graphic object data, and may contain size information, suchas a width and a height, or color table information of a pertinentobject. The size information and color table information will not bedescribed in detail, but may be included in a separate segment of thedisplay set 120 a, 120 b . . . or 120 n. The ODSs 122 a through 122 nalso include the PTS information thereof. The PTS information of the ODS122 through 122 n indicates when the ODSs 122 a through 122 n are storedin a first buffer 233 of the graphic data processing apparatus 230. TheEND 123 indicates the end of one display set 120 a, 120 b . . . or 120n.

Two types of presentation information exist. That is, when graphic dataand page composition information which defines a page composition of thegraphic data, one type of presentation information indicates whengraphic screen data exist, which is composed with reference to the pagecomposition information of the graphic data, is output to the displayscreen. The presentation information is recorded in the page compositionsegment (PCS) 121 including the page composition information.

When a graphic object of which the graphic data screen is composed,another type of the presentation information indicates when the graphicobject is decoded in a decoder and is outputted. If a time taken todecode the graphic object in the decoder is 0, the presentationinformation may be considered as being information indicating when thegraphic object is input to the decoder to be decoded.

FIG. 2 is a block diagram of a graphic data processing apparatus 230 forprocessing graphic data according to a second embodiment of the presentinvention.

The graphic data processing apparatus 230 includes a coded data buffer231, a decoder 232, a first buffer 233, a second buffer 234, a pagecomposition buffer 235 and an image controller 236.

The subtitle graphic stream and the navigation graphic stream, which arestored in a form of an MPEG-2 TS in the information storage medium, passthrough a read buffer (not shown) and a source de-packetizer (not shown)in which an arrival time stamp (ATS) that had been added to the MPEG-2TS is removed, and further, are input to a transport packet identifier(PID) filter 210 in the form of an MPEG-2 TS packet. Input timing of afirst byte of the MPEG-2 TS packet input to the PID filter 210 isdetermined by ATS information contained in a first header of the MPEG-2TS packet. Further MPEG-2 TS packets are input to the PID filter 210according to a TS_recording_rate.

The PID filter 210 determines, with reference to a PID of the MPEG-2 TSpacket, whether or not the input MPEG-2 TS packet has a desired PIDvalue, and transmits MPEG-2 TS packets having the desired PID values toa transport buffer 220. Since buffering and delay do not theoreticallyoccur in the PID filter 210, the MPEG-2 TS packets are outputimmediately after being input to the PID filter 210.

The transport buffer 220 receives an MPEG-2 TS packet having a specificPID value output from the PID filter 210. That is, the transport buffer220 performs a queue operation to temporarily store the MPEG-2 TS packetbefore the MPEG-2 TS packet is input to the graphic data processingapparatus 230. Once the MPEG-2 TS packet is input to the transportbuffer 220, a header of the MPEG-2 TS packet and a header of aPacketized Elementary Stream (PES) packet are removed. Further,referring to FIG. 1, the header 110 of the MPEG-2 TS packet for thesubtitle graphic data and navigation graphic data includes PTSinformation. After the header of the MPEG-2 TS packet is removed, thePTS information indicates when the data packet 120, including of thedisplay sets 120 a, 120 b . . . and 120 n shown in FIG. 1, is input tothe coded data buffer 231.

The coded data buffer 231 receives the subtitle graphic data stream andthe navigation graphic data stream in a coded state and buffers thesubtitle graphic data stream and the navigation graphic data stream thatare to be processed in the graphic data processing apparatus 230. Thesubtitle graphic data stream and the navigation graphic data streaminput to the coded data buffer 231 are output from the coded data buffer231 according to the PTS information included in the ODS 122 a through122 n.

The PTS information of the ODS 122 a through 122 n is, for example,information indicating when a storage of the ODS 122 a through 122 n inthe first buffer 233 ends, since an ideal decoding time of the graphicdata in the decoder 232 is 0. That is, a time when the ODS 122 a through122 n is output from the coded data buffer 231 is equal to a time whenthe ODS 122 a through 122 n is stored in the first buffer 233. The PTSinformation of the ODS 122 a through 122 n indicates not only the timewhen the ODS 122 a through 122 n is output from the coded data buffer231, but also the time when the ODS 122 a through 122 n is stored in thefirst buffer 233 after being decoded. However, since it actually takessome time for the decoder 232 to decode the ODS 122 a through 122 n, thePTS information of two ODSs, for example, ODS 122 a and 122 b, have apredetermined time interval therebetween in consideration of a timerequired for the decoder 232 to decode a previous object.

The decoder 232 decodes the input subtitle graphic data and inputnavigation graphic data. After the input subtitle and input navigationgraphic data are decoded, the decoded PCS 121 is output to the pagecomposition buffer 235 and the decoded ODS 122 a through 122 n is outputto the first buffer 233. Theoretically, a time taken to decode the inputdata in the decoder 232 is 0. Thus, the decoding operation is called aninstant decoding operation.

The page composition buffer 235 stores the PCS 121 which is decoded andoutput from the decoder 232.

The first buffer 233 stores the ODS 122 a through 122 n, which isdecoded in the decoder 232, according to object identifier object_id ofthe ODS 122 a through 122 n. Since the decoded object data is stored inthe first buffer 233, one object is reusable several times before thefirst buffer 233 is completely reset.

The second buffer 234 stores data right before graphic screen data of ascreen, which is composed of graphic data objects necessary to displaythe subtitle graphic data and the navigation graphic data on the displaydevice, is output. The data stored in the second buffer 234 is output tothe display device according to the PTS information of the PCS 121having page composition information of a pertinent page.

The image controller 236 controls, with reference to object identifiers(i.e., object_id), objects to be transmitted from the first buffer 233to the second buffer 234 and to be displayed on one page. That is, theimage controller 236 controls the first buffer 233 to select the graphicdata object necessary to compose the pertinent page (i.e. screen), basedon the page composition information of the PCS data output from the pagecomposition buffer 235, and to transmit selected graphic data objectfrom the first buffer 233 to the second buffer 234. The image controller236 transmits the page composition information to the second buffer 234to compose the display screen. Further, when the image controller 236receives a user command from a user, the image controller 236 controlsthe above elements to select the subtitle graphic data and thenavigation graphic data having a different PID and composes a displayscreen.

FIG. 3 is a diagram illustrating a third embodiment of the presentinvention of graphic data.

An operation of processing the graphic data having display sets 120 athrough 120 n in a graphic data processing apparatus 230 and displayingthe processed graphic data on a display screen will be explained indetail with reference to FIG. 3.

Referring to FIG. 3, subtitle graphic data and navigation graphic datahave four display sets 305 through 320, 325 through 330, 335 through345, and 350 through 360. As an MPEG-2 TS including a plurality ofdisplay sets passes through the decoder 232, the subtitle graphic dataand the navigation graphic data included in the ODS 122 a through 122 nis stored in the first buffer 233 and the page composition informationcontained in the PCS 121 is stored in the page composition buffer 235.Further, both the graphic data and the page composition information aretransmitted to the second buffer 234 based on respective PTSinformation. The operation will be explained below. A header of eachdisplay set is not shown in FIG. 3 for convenience of description.

FIG. 4A is a diagram illustrating a state in which a first display set305 through 320 having a PCS 305 with a page_id=1 is stored in buffers.

Graphic data of an ODS 310 with an object_id=1 and graphic data of anODS 315 with the object_id=2 are stored in the first buffer 233 at atime indicated by the PTS information included in the ODSs 310 and 315.At this time, no data is stored in the page composition buffer 235. Ingeneral, an instance where all object data stored in the first buffer233 is no longer used and a new display set is input to the first buffer233 to process new object data is called mode conversion. A first PCSinput during mode conversion has no data or is a dummy PCS. Accordingly,a graphic data processing apparatus 230 decodes only necessary objectsof the first display set 305 through 320 until a subsequent modeconversion and stores the necessary objects in the first buffer 233.Therefore, there is no data in the second buffer 234.

FIG. 4B is a diagram illustrating a state in which a second display set325 through 330 having a PCS 325 with the page_id=2 is stored in thebuffers.

Referring to FIG. 3, the second display set 325 through 330 having thePCS 325 with the page_id=2 includes the PCS 325 and an END 330. Thesecond display set 325 through 330 includes the page compositioninformation to display the objects of the first display set 305 through320 with the page_id=1 stored in the first buffer 233 on the displayscreen. Accordingly, the PCS 325 with the page_id=2 includes positioninformation indicating which graphic objects are displayed and where thegraphic objects are displayed on the display screen. The imagecontroller 236 controls the first buffer 233 using the page compositioninformation of the PCS 325 with the page_id=2 so that the graphicobjects corresponding to the ODS 310 with the object_id=1 and the ODS315 with the object_id=2 are transmitted to the second buffer 234 andthe screen may be composed. At a time indicated by the PTS informationincluded in the PCS 325, graphic screen data of a completely composedscreen is output from the second buffer 234 to the display device.

FIG. 4C is a diagram illustrating a state in which a third display set335 through 345 having a PCS 335 with the page_id=3 is stored in thebuffers.

Referring to FIG. 3, the third display set 335 through 345 having thePCS 335 with the page_id=3 includes the PCS 335, an ODS 340 with theobject_id=2, and an END 345. The ODS 340 included in the third displayset 335 through 345 having the PCS 335 with the page_id=3 has a commonobject_id as that of the ODS 315 of the ODSs 310 and 315 of the firstdisplay set 305 through 320 having the PCS 305 with the page_id=1. Sincethe ODS 340 having the common object_id as that of the ODS 315 overliesthe ODS 315, the ODS 340 consequently performs an update operation. Thatis, although the page composition information of the PCS does notchange, an updated object is reflected on the display screen such thatat a time indicated by PTS information of the pertinent PCS, graphicdata, which is stored in the second buffer 234, of a completely composedscreen is output to the display device.

FIG. 4D is a diagram illustrating a state in which a fourth display set350 through 360 having a PCS 350 with the page_id=4 is stored in thebuffers.

Referring to FIG. 3, the fourth display set 350 through 360 having thePCS 350 with the page_id=4 includes the PCS 350 containing new pagecomposition information, an ODS 355 with the object_id=3, and an END360. After the graphic processing apparatus 230 stores datacorresponding to each segment in the first buffer 233, the second buffer234, and the page composition buffer 235, the graphic processingapparatus 230 outputs data, which is stored in the second buffer 235, ofa completely composed screen to the display device at a time indicatedby PTS information of the PCS 350 with the page_id=4.

FIGS. 5A-5D are diagrams illustrating a process of inputting andoutputting data to and from the buffers in accordance with a passage oftime.

Referring to FIGS. 5A-5D, all of the PCS 305, ODS 310 and 315 and END320 of the first display set 305 through 320 are stored in the codeddata buffer 231 at a time 510 indicated by PTS information included inan MPEG-2 TS header of a pertinent packet, and are output from the codeddata buffer 231, decoded in the decoder 232, and stored in the firstbuffer 233 at time 550 and at time 560 indicated by PTS information ofthe respective ODSs 310 and 315. As previously explained, a time whenone object is output from the coded data buffer 231 theoretically isequal to a time when the object is decoded in the decoder 232 and storedin the first buffer 233. However, in actuality, since time is taken todecode the object, the value of the time 560 indicated by the PTSinformation of the ODS 315 with the object_id=2 is greater than that ofthe time 550 indicated by the PTS information of the ODS 310 with theobject_id=1.

Accordingly, a first graphic object of the ODS 310 with the object_id=1is output from the coded data buffer 231 and is decoded and stored inthe first buffer 233 at the time 550 indicated by the PTS information ofthe ODS 310 with the object_id=1. A second graphic object of the ODS 315with the object_id=2 is output from the coded data buffer 231, and thendecoded and stored in the first buffer 233 at the time 560 indicated bythe PTS information of the ODS 315 with the object_id=2.

All the PCS 325 and END 330 of the second display set 325 through 330are stored in the coded data buffer 231 at a time 520 indicated by PTSinformation included in a header of the pertinent packet. The PCS 325 isdecoded in the decoder 232 and stored in the page composition buffer235. The image controller 236 controls the first buffer 233 to transmitthe object necessary to compose the pertinent screen from the firstbuffer 233 to the second buffer 234 based on the page compositioninformation. A time when the object stored in the first buffer 233 istransmitted to the second buffer 234 and the screen composition starts,is the same as a time indicated by the PTS information of the ODS, whichis stored last in the first buffer 233.

However, since the PCS 305 of the first display set 305 through 320 is adummy PCS with no page composition information, the ODS 315 with theobject_id=2, which is stored last, is not transmitted to the secondbuffer 234 at the time indicated by the PTS information thereof, and notused in the screen composition. When the image controller 236 uses thePCS information of the second display set 325 through 330 which isdecoded and stored in the page composition buffer 235, the first graphicobject with the object_id=1 and the second graphic object with theobject_id=2, which are necessary for the screen composition, aretransmitted from the first buffer 233 to the second buffer 234 such thatthe screen composition starts. At a time 590 indicated by PTSinformation of the PCS 325 with the page_id=2, the graphic screen dataof a completely composed screen is output to the display screen.

All of the PCS 335, ODS 340, and END 345 of the third display set 335through 345 are stored in the coded data buffer 231 at a time 530indicated by PTS information included in a header of the pertinentpacket and are output from the coded data buffer 231, decoded, andimmediately stored in the first buffer 233 at a time 570 indicated bythe PTS information of the ODS 340 of the third display set 335 through345. At this time, since the ODS 340 included in the third display set335 through 345 uses a common object_id as that of the ODS 315, whichhas already been stored in the first buffer 233, the ODS 340 overliesthe previously stored second object of the ODS 315. As a result, anupdated second object is obtainable.

However, since the PCS 335 with the page_id=3 performs the screencomposition using the ODSs 310 and 340 with the object_id=1 and theobject_id=2, the ODS 340 with the object_id=2 is stored last in thefirst buffer 233 at the time indicated by the PTS information of the ODS340, and is simultaneously transmitted to the second buffer 234 to beused in the screen composition. At a time 591 indicated by the PTSinformation of the PCS 335 with the page_id=3, a page of a completelycomposed screen is output to the display device. At this time, thesecond buffer 234 maintains a display screen output which is composedbased on the page composition information of the PCS 325 with thepage_id=2 until the time indicated by the PTS information of the PCS 335with the page_id=3.

Furthermore, all of the PCS 350, ODS 355, and END 360 of the fourthdisplay set 350 through 360 are stored in the coded data buffer 231 at atime 540 indicated by the PTS information included in a header of thepertinent packet and are output from the coded data buffer 231, decoded,and immediately stored in the first buffer 233 at a time 580 indicatedby the PTS information of the ODS 355 of the fourth display set 350through 360. At a time 592 indicated by the PTS information of the PCS350 with the page_id=4, a page of a completely composed screen is outputto the display device. At this time, the second buffer 234 maintains adisplay screen output which is composed based on the page compositioninformation of the PCS 335 with the page_id=3 until the time indicatedby the PTS information of the PCS 350 with the page_id=4. Accordingly,the second buffer 234 includes a preparing buffer 610 and a displaybuffer 620 as shown in FIG. 6.

FIG. 6 is a detailed block diagram of the second buffer 234.

Referring to FIG. 6, the second buffer 234 includes the preparing buffer610 and the display buffer 620. The preparing buffer 610 is a memoryused in placing, with reference to the page composition information,objects input from the first buffer 233 at predetermined positions ofthe display screen. The display buffer 620 is a memory used indisplaying data of the prepared display screen. At a time indicated bythe PTS information of the PCS 305, 325, 335 and 350, operations of thepreparing buffer 610 and the display buffer 620 are exchanged and dateof the completely composed screen is finally output to a disply device630.

In further detail with reference to FIGS. 4B and 4C, when the screencomposition is completed with reference to the information of the PCS325 with the page_id=2, contents of the second buffer 234 of FIG. 4B arestored in the display buffer 620, and output to the display device 630.Screen composition proceeds in the preparing buffer 610 with referenceto the information of the PCS 325 with the page_id=3. At the timeindicated by the PTS information of the PCS 335 with the page_id=3, theoperations of the preparing buffer 610 and the display buffer 620 areexchanged such that the contents of the second buffer 234 shown in FIG.4C are output to the display device 630 and the data of the fourthdisplay set 350 through 360 is input to the preparing buffer 610 in acommon manner as described above so as to be used in the screencomposition.

FIG. 7 is a flow chart illustrating an operation of outputting graphicdisplay data of a completely composed page to the display device.

In operation S710, graphic data is received. In operation S720, pagecomposition information which describes a page composition of thegraphic data is received. In operation S730, graphic screen data whichis composed with reference to the page composition information of thegraphic data is output to the display screen according to presentationinformation which indicates when the graphic screen data is output tothe display screen. The presentation information is recorded in a pagecomposition segment including the page composition information. Further,if a plurality of graphic data values exists, a graphic display screencomposition starts with reference to the presentation information of arespective one of the graphic data values, among the plurality ofgraphic data values, that was last input.

FIG. 8A is a flow chart illustrating an operation of outputting adecoded graphic object.

In operation S810, a graphic object of which a graphic data screen iscomposed is received. In operation S820 a, a decoded graphic object isoutput according to presentation information indicating when the graphicobject is decoded and output.

FIG. 8B is a flow chart illustrating an operation of inputting a graphicobject to the decoder.

In operation S810, a graphic object of which a graphic screen iscomposed is received. In operation S820 b, the graphic object is inputto the decoder 232 to be decoded according to presentation informationindicating when the graphic object is input to the decoder 232.

In theory, assuming that a decoding time in the decoder 232 is 0, FIGS.8A and 8B show that a time when the graphic object is input to thedecoder 232 is the same as a time when the graphic object is output fromthe decoder 232. The presentation information is recorded in an objectdisplay segment having the graphic object. Thus, according to theinvention, if a plurality of graphic objects exist, respective timevalues indicated by presentation information of the graphic objects havea predetermined time interval therebetween.

This invention may be embodied in a general purpose digital computer byrunning a program from a computer-readable medium, including but notlimited to, storage media such as magnetic storage media (e.g., ROMs,floppy discs, hard discs, etc.), optically readable media (e.g.,CD-ROMs, DVDs, etc.), and carrier waves (e.g., transmissions over theInternet). The computer-readable medium may be dispersively installed ina computer system connected to a network, and stored and executed ascomputer-readable code by a distributed computing environment.

As described above, if graphic data composition information andpresentation information are used, a graphic object is reusable duringgraphic data processing. Accordingly, a time taken to process graphicdata is reducible and memory area may be saved.

Although a few embodiments of the present invention have been shown anddescribed, it would be appreciated by those skilled in the art thatchanges may be made in this embodiment without departing from theprinciples and spirit of the invention, the scope of which is defined inthe claims and their equivalents.

1. An apparatus for processing graphic data, the apparatus comprising: afirst buffer to store graphic object data defining a graphic object fora predetermined time so that the graphic object data remains availablefor use for the predetermined time; and a second buffer to storecomposition information for the graphic object defined by the graphicobject data stored in the first buffer, the composition informationspecifying how the graphic object is to be displayed on a displaydevice.
 2. The apparatus of claim 1, wherein the graphic object data isidentified by an object identifier.
 3. The apparatus of claim 1, whereinthe first buffer stores the graphic object data until the first bufferis reset.